The present invention relates to the field of communications and more particularly to radiotelephone communications methods and systems.
Conventional cellular communications systems (such as systems operating according to the IS-136 standard) generally provide one-to-one communications from one mobile terminal to another mobile terminal or to a landline telephone coupled to a public switched telephone network. A conventional cellular communications system is illustrated in FIG. 1. This system includes a mobile switching center (MSC) 31 and a home location register 33.
The MSC is coupled to a plurality of radio base stations (RBS) 32 wherein each RBS 32 defines a cell 35. In addition, the MSC can be coupled to a public switched telephone network (PSTN) 36. As will be understood by those having skill in the art, the conventional cellular communications system of FIG. 1 can provide cellular radiotelephone communications for one or more cellular mobile terminals (MT) 37. More particularly, the cellular radiotelephone communications can be provided using conventional cellular standards wherein a telephone is dialed to place a call to another communications device.
Each RBS provides radio frequency transmit and receive functions and supports low level protocol functions. Moreover, a RBS can be considered a dumb peripheral of the MSC 31 wherein the MSC provides central intelligence for the system. Each RBS can be coupled to the MSC 31 via communications links 39. These communications links can be T1 links provided, for example, via landline or microwave. The MSC 31 provides voice path switching between two cells or a cell and the PSTN 36. The MSC 31 provides central system intelligence to control the radio base stations and to process high level protocol messages from mobile terminals 37 relayed by the radio base stations. In other words, the MSC handles call setup, paging, handoff, and call connection.
The home location register 33 keeps track of the current status of the mobile terminals. For each mobile terminal, for example, the home location register can record whether that terminal is on, off, or busy, as well as the location area (including a group of cells) within which the mobile terminal is located. The home location register can also include a database of restrictions and allowed service features for each mobile terminal. The home location register can also be considered a portion of the MSC.
The setup of a call between mobile terminals 37 using the system of FIG. 1 is illustrated in FIG. 2. As shown, the originating mobile terminal 37a issues an origination message which is received by the radio base station 32a for the cell 35a in which the mobile terminal 37a is located. The radio base station 32a checks the origination message for errors, and if no significant errors are detected, the radio base station 32a forwards the message to the mobile switching center. The mobile switching center authenticates the originating mobile terminal 37a and analyses the called number. If the originating mobile terminal and the called number are valid, the mobile switching center instructs the radio base station 32a to assign a Digital Traffic Channel (DTC) to the originating mobile terminal. Origination and channel designation messages are discussed, for example, in TR45, TIA, EIA-136-123-A Draft Text, Digital Control Channel Layer 3, Aug. 31, 1998, the disclosure of which is hereby incorporated herein in its entirety by reference.
Because the called party is another mobile terminal, the mobile switching center checks the HLR to determine the current location area (LA) for the called mobile terminal 37b if the called mobile terminal is active. A plurality of cells is assigned to a location area, and a mobile terminal updates its location with the cellular system only when the mobile terminal enters a new location area. Accordingly, location area updates are not needed every time a mobile terminal enters a new cell. While Digital Control Channel (DCCH) traffic may be reduced, pages for a called mobile terminal may need to be transmitted in all cells assigned to the location area.
The mobile switching center then issues a page message to all radio base stations supporting cells in the location area of the called mobile terminal 37b. Each of these radio base stations issues a page message on an appropriate paging subchannel. Because of the DCCH paging structure, however, a period of time as long as 1.28 seconds may pass before the page message can be issued. The page message wakes the called mobile terminal from its battery sleep mode, and the called mobile terminal 37b responds to the appropriate radio base station (now referred to as the called radio base station 32b) with a page response message to indicate the same.
The page response message is relayed from the called radio base station 32b to the mobile switching center, and the mobile switching center instructs the called radio base station 32b to assign a digital traffic channel to the called mobile terminal 37b. The mobile switching center then completes a communications path between the originating mobile terminal 37a and the called mobile terminal 37b using the two digital traffic channels.
Pages transmitted from the cellular communications system to a mobile terminal can be transmitted over a digital control channel (DCCH) as shown in FIG. 2B. For example, the page transmitted by the radio base station to the terminal 37b of FIG. 2A can be transmitted over the digital control channel of FIG. 2B. In particular, the digital control channel can be a time division multiple access (TDMA) control channel including a plurality of time slots T0 to T31 grouped into time frames so that each time frame includes a plurality of sequential time slots. According to the IS-136 standard, each super frame can include 32 time slots. Moreover, the time frames can be organized into a hyperframe structure with a primary superframe and a secondary superframe included in each hyperframe with each secondary superframe repeating the information transmitted during the preceding primary superframe. Accordingly, a mobile terminal typically has two opportunities to receive information transmitted over the digital control channel of FIG. 2B.
A page can thus be transmitted to a mobile terminal during one of the 32 time slots of the primary superframe and then retransmitted during the corresponding time slot of the secondary superframe. To save power at the mobile terminal, the mobile terminal is assigned a time slot over which pages for the mobile terminal will be transmitted. Accordingly, the mobile terminal need only monitor the assigned time slot in each superframe, and the mobile terminal receiver can be powered down during the other time slots. In the example of FIG. 2B, the mobile terminal 37 is assigned time slot T12 so that pages for the mobile terminal are transmitted during the twelfth time slot of a frame. The mobile terminal receiver can thus be turned off during time slots T0-T11 and T13-T31 of each time frame thereby reducing power consumption and increasing battery life. Moreover, if a page for the mobile terminal is correctly received during the assigned time slot of a primary superframe, the mobile terminal receiver can be turned off during the entirety of the subsequent secondary superframe.
A control channel paging time slot is typically assigned to the mobile terminal within a cell of a cellular communications system using a hashing algorithm based on a mobile identification number (MIN) for the mobile terminal. According to the IS-136 standard, this hashing algorithm is independently executed by both the mobile terminal and the radio base station for the cell so that the assignment of the time slot is not communicated between the mobile terminal and the radio base station. The hashing algorithm typically is designed to distribute mobile terminals within a cell across the time slots of a digital control channel frame for the cell thereby balancing the load on the digital control channel.
For example, a page for the mobile terminal 37 received by a radio base station from a mobile switching center may include the mobile identification number for the mobile terminal, and the radio base station can use the hashing algorithm to determine that the page should be transmitted over time slot T12. The mobile terminal knows to monitor time slot T12 based on a separate execution of the hashing algorithm. The mobile terminal can perform the hashing algorithm using the mobile identification number as well as base station specific information transmitted by the base station over a broadcast control channel (BCCH). For example, the number of slots available for paging over the digital control channel (DCCH) may vary by base station so that the number of paging time slots for the hashing algorithm may vary by base station.
The conventional cellular communications system of FIG. 1, however, may not support dispatch oriented group calls (also referred to as conference calls). Radio dispatch group communications systems are commonly used by emergency service providers such as police and/or fire departments to provide communications between a dispatcher and emergency personnel. For example, a police dispatcher can simultaneously call all on-duty police officers using a radio dispatch communications system. Alternately, a police officer can quickly establish communications with other police officers and/or dispatchers simply by pressing a push-to-talk button on his radio. Similar radio dispatch communications systems may also be used by businesses such as trucking and/or taxi businesses.
In general, radio dispatch group communications systems provide one-to-many group communications as opposed to one-to-one communications provided by conventional cellular radiotelephone communications systems. Radio dispatch group communications are also preferably provided without the call setup delays that may be common in a conventional cellular radiotelephone communications system. For example, the time required to setup a call in a conventional IS-136 cellular radiotelephone system may be as long as 6 or 7 seconds including up to 1.28 seconds just to page the receiving cellular radiotelephone. This setup time, however, may be unacceptable for police and other emergency radio dispatch group communications systems.
With the proliferation of cellular communications systems, there has been an effort to provide hybrid communications systems that can support both cellular radiotelephone communications as well as dispatch oriented group communications. Such a system has been developed, for example, by Motorola, with service being offered by Nextel. A similar system has been developed by Ericsson (the assignee of the present application) under the name DAMPS-PRO. In particular, the DAMPS-PRO product provides cellular communications according to the IS-136 cellular communications standard, as well as dispatch oriented group communications for predefined user groups.
In the DAMPS-PRO system, intelligent group communications functionality is added to an IS-136 cellular communications system as shown in FIG. 3. This intelligent group communications functionality is provided by adding a group server 41, a group bridge 43, a local area network 45, and a group database 47. The cells, mobile switching center, home location register, public switched telephone network, and radio base stations provide cellular communications as discussed above with regard to FIGS. 1 and 2.
With regard to group calls, the group bridge provides a bank of telephony equipment which can initiate and receive radiotelephone calls, provide voice prompts, and respond to user inputs. The bridge also provides a group function that sums the audio from all parties within a designated group and distributes the summed audio to all parties. The server communicates with the mobile switching center via standard telephony signaling (such as defined by the SS7 standard) and controls the operation of the bridge equipment via the local area network.
The setup for a group call according to the DAMPS-PRO system is illustrated in FIG. 4. In general, a predetermined set of mobile terminals define a group which can communicate in the group call mode. Each of these mobile terminals may have standard cellular radiotelephone functionality whereby one-to-one communications can be provided after entering a telephone number and pressing a send button. Mobile terminals in a conference group may also include a push-to-talk (PTT) button which can automatically establish a group call with other active mobile terminals in the group.
In particular, an originating mobile terminal 37axe2x80x2 may issue an origination message when the PTT button is pushed. The radio base station providing service to the originating mobile terminal 37axe2x80x2 (now referred to as the originating radio base station 32axe2x80x2) receives the origination message, and checks the origination message for errors. If no significant errors are detected, the origination message is forwarded to the mobile switching center. The mobile switching center authenticates the originating mobile terminal 37axe2x80x2 and analyses the called number therein identifying the group. If the originating mobile terminal 37axe2x80x2 and the identified group are valid, the mobile switching center authorizes the originating radio base station 32axe2x80x2 to assign a digital traffic channel to the originating mobile terminal 37axe2x80x2, and a conversation channel is established between the originating mobile terminal 37axe2x80x2 and the group bridge 43 using the assigned digital traffic channel.
Group calls are indicated by a Called party number portion of the origination message that is understood by both the mobile terminals in the group and the mobile switching center. The mobile switching center detects that the called party number is for a group call and connects the originating mobile terminal to the conference bridge. The conference server accepts the call and then searches the group database to determine the other mobile terminals in the group that should be called. The server then instructs the conference bridge to place calls to each of the other mobile terminals in the group via the mobile switching center. The call from the originating mobile terminal and the calls to each of the other mobile terminals in the group are then grouped together. In particular, the mobile switching center issues pages for each of the other mobile terminals in. the group and completes each call normally once each serving radio base station is known. As further shown in the flow diagram of FIG. 5, the steps of sending the origination message at block 81, setting up the originating side of the call at block 83, paging to locate the called mobile terminals at block 85, and setting up the terminating side of the call at block 87 proceed sequentially.
In the hybrid communications system discussed above, a hybrid terminal may need to monitor a digital control channel for individual pages identified by the mobile identification number intended for the terminal only as discussed above with regard to FIG. 2B. In addition, the hybrid terminal may need to monitor the digital control channel for group pages identified by a group identification number. The hybrid terminal may thus need to monitor two different time slots in each digital control channel frame, thereby increasing the amount of time the mobile terminal receiver is powered up during each control channel frame, increasing the power consumed, and increasing the drain on the mobile terminal battery. Accordingly, there continues to exist a need in the art for methods, systems, and terminals providing improved paging and providing reduced power consumption.
It is therefore an object of the present invention to provide improved methods, systems, and terminals for group communications.
It is another object of the present invention to provide cellular communications methods, systems, and terminals that can improve group paging.
It is another object of the present invention to provide cellular communications methods, systems, and terminals that can reduce power consumption.
It is still another object of the present invention to provide communications methods, systems, and terminals that can increase access speeds.
These and other objects can be provided according to the present invention by defining control channel including a plurality of time slots wherein the time slots are grouped into time frames so that each time frame includes a plurality of sequential time slots. A first time slot of each of the time frames is assigned as a first paging channel for one of the terminals. In addition, a second time slot of each of the time frames is assigned as a second paging channel for the terminal, wherein the second time slot is assigned to provide a desired proximity of the first and second time slots within each of the time frames. The mobile terminal receiver can thus be powered up for an interval of time during a control channel frame including the first and second time slots of the frame and powered down during the remainder of the frame. By providing the first and second time slots within the desired proximity, the interval of time over which the receiver is powered up during each frame can be reduced, thereby reducing power consumed by the mobile terminal and increasing mobile terminal battery life.
More particularly, the second time slot can be assigned to provide the second time slot within a predetermined number of time slots of the first time slot within each of the time frames. Preferably, the second time slot is assigned to be the same as the first time slot so that the mobile terminal needs to monitor only one time slot of a control channel frame. In addition, the step of assigning the second time slot can include determining whether the second time slot can be provided within a predetermined number of time slots of the first time slot, and responsive to determining that the second time slot can be provided within the predetermined number of time slots of the first time slot, assigning the second time slot within the predetermined number of time slots of the first time slot within each of the time frames. Alternately, the second time slot can be assigned so that at least a second predetermined number of time slots separates the first and second time slots within a time frame wherein the second predetermined number of time slots is greater than the first predetermined number of time slots, responsive to determining that the second time slot cannot be provided within the predetermined number of time slots of the first time slot.
A third time slot of each of the time frames can be assigned as a third paging channel for a second one of the terminals, and a fourth time slot can be assigned as a fourth paging channel for the second terminal wherein the fourth time slot is assigned to provide a desired proximity of the third and fourth time slots within each of the time frames. In addition, relative high and low priorities can be assigned to the first and second terminals respectively so that the desired proximity of the first and second time slots is given higher priority than the desired proximity of the third and fourth time slots. In other words, the assignments for the mobile terminal having the high assignment priority can be made preferentially. More particularly, the relative high priority can be assigned to a mobile terminal having a low battery charge and/or a preferred status such as a terminal for a police or fire department.
In addition, the first and second terminals can provide group communications therebetween, and the second and fourth time slots can comprise a common time slot so that the second and fourth paging channels comprises a common group paging channel. The relative high and low priorities can thus be assigned to the first and second terminals so that the desired proximity of the first time slot and the common time slot is given higher priority than the desired proximity of the third time slot and common time slot. When two mobile terminals providing group communications therebetween are in a common cell, the common time slot can thus be used to transmit group pages for the group including the first and second terminals.
More particularly, the control channel can be a digital control channel such as a time division multiple access (TDMA) digital control channel according to the IS-136 standard. Moreover, the first and second consecutive time frames can define respective primary and secondary frames such that information included in the secondary frame is the same as information included in the primary frame. The first paging channel for the terminal can be an individual paging channel for the terminal and the second paging channel can be a group paging channel for the terminal. In addition, the first time slot can be assigned based on an identification number for the terminal according to a hashing algorithm. The identification number can be, for example, a mobile identification number (MIN) according to the IS-136 standard.
The assignment of the time slots can be preceded by communicating a login message from the terminal to the communications system, and followed by communicating at least one of the first time slot assigned as the first paging channel and the second time slot assigned as the second paging channel from the communications system to the terminal. At least one of the time slots can thus be assigned independently by the radio base station servicing the cell within which the mobile terminal is located responsive to the login message and then transmitted to the respective mobile terminal. Accordingly, the radio base station can assign at least one of the time slots to provide the desired proximity/and based on current control channel traffic without requiring a parallel calculation at the mobile terminal. Instead, the assignment is transmitted to the mobile terminal.
The methods, systems and terminals of the present invention can thus provide time slot assignments for group and individual pages for a mobile terminal to reduce power consumption and the resulting battery drain at the mobile terminal. More particularly, first and second time slots for group and individual pages can be assigned to provide a desired proximity therebetween within a control channel time frame thereby allowing the mobile terminal receiver to be powered up over a period of time including both time slots while reducing the period of time that the receiver is powered up during a time frame.